Influence of Frequency and Anodic Effect Duration on the Vanadium Concentration in the Aluminium Obtained by Electrolysis of Cryolite-Alumina Melts

摘要

Some data in aluminium electrolysis cells show thai though the same raw materials and anodes were used in all cells, however the impurities concentration in metallic aluminium differ from one cell to another. This is also the case of vanadium that enhances the electrical resistivity of aluminium, it is therefore a harmful impurity. Data collected from 4 industrial cells for aluminium electrolysis showed that vanadium concentration in aluminium is in inverse ratio to the product between anodic effect duration and medium voltage during anodic effect. It is known that during the anodic effect a great amount of energy arises in electrolysis celts and also an increased amount of carbon dust is formed. Due to temperature rise, vanadium salts vaporize and are also adsorbed on the surface of carhon dust particles. Carbon in the electrolyte oxidizes and leaves the melt with anodic gases, thus explaining the decrease of vanadium concentration in aluminium together with the increase of anodic effect frequency. It has been observed also that the carbon anodes consumption during electrolysis increases together with the increase of vanadium concentration In the anode. This is due to the fact that vanadium catalyzes the carbon oxidation reaction.